An active matrix liquid crystal display displays a motion picture using a thin film transistor (TFT) as a switching element. The liquid crystal display may be made to be smaller and more compact than a cathode ray tube (CRT) and thus may be applied to display units of portable information appliances, office equipments, computers, etc. Further, the liquid crystal display may be applied to televisions and thus is rapidly replacing the cathode ray tube.
A transmission type liquid crystal display occupying most of the liquid crystal displays controls an electric field applied to a liquid crystal layer and modulates light coming from a backlight unit, thereby displaying an image. The image quality of the liquid crystal display depends on contrast characteristics. It is limited to an improvement of the contrast characteristics using only a method for controlling a data voltage applied to the liquid crystal layer to modulate a light transmittance of the liquid crystal layer. Accordingly, a backlight dimming method for controlling brightness of light sources of the backlight unit based on an input image was proposed so as to further improve the contrast characteristics.
Examples of the backlight dimming method include a global dimming method for controlling a luminance of an entire display surface and a local dimming method for locally controlling the luminance of the display surface. The global dimming method may improve a dynamic contrast measured between two successively arranged frames. The local dimming method locally controls the luminance of the display surface during one frame, thereby improving a static contrast which has difficulty in being improved through the global dimming method.
The related art local dimming method divides input digital video data in conformity with virtual blocks divided from a display screen of a liquid crystal display panel in a matrix form, obtains a representative value of the input digital video data of each block, and adjusts a dimming value of each block based on the representative value of each block, thereby controlling the brightness of the light sources belonging to each block in the backlight unit. The related art local dimming method increases a driving current supplied to the light sources and/or a length of a supply period of the driving current, thereby increasing the brightness of the light sources. However, when the driving current and/or the length of the supply period of the driving current increase without limit so as to increase the brightness of the light sources, an increase in power consumption is caused.